Livin’ Large

As a technology, injection molding is over sixty years old, and while the basics of reciprocating screw technology have matured over the years, the desire for ever larger parts is accelerating. “Large” is a relative concept, but several manufacturers now offer injection molding equipment in the 5000 ton class and larger. Thinking of joining the elite club of Canadian super-size part molders? Much of a molder’s existing knowledge will translate with large presses, but some of the details are novel. And as the old saying goes, the devil is in the details.

What’s best?

Peter Stephen, president of Stephen Sales Ltd., has some strong opinions about the proliferation of designs in the large tonnage injection molding segment: “Three years ago at NPE, there were 10 manufacturers who introduced and showed large machines, and every machine was different. They are where hydraulic clamp machines were 15 years ago, before they evolved into the same design. These 10 will probably evolve into one or two. Technology is back on the table.”

Two-platens lead

Engel defines a large tonnage machine as 500 tons and up, says vice-president sales and marketing Kurt Fenske, although he allows current market perception of “large” is now moving to even higher tonnages. Engel’s sales of large tonnage presses is market-driven, with over 60 percent being delivered to automotive OEMs and Tier One suppliers. The remainder of Engel’s large-tonnage sales is mostly to the electronics market, with a small segment also going to the housewares industry.

Fenske is adamant about the direction of technology in the large tonnage market: “Two-platen technology is dominant across all sizes. Also, I don’t think you can sell a large machine today without a robot.”

Two-platen designs existed some thirty years ago, without widespread success, but in modern large press applications, the smaller footprint, speed, and lower power and oil demands has made two platen a front-runner.

Helmut Hock, general manager of large tonnage machines for Husky Injection Molding Systems Ltd., is enthusiastic about the new breed of two-platen machines: “There’s no doubt that two-platen technology in large tonnage machines is here to stay. You get significant floor space savings. And with recent technological advances in Husky machines, you get the space (advantage) and ease of maintenance. It’s a win-win.” Husky currently builds the world’s largest two-platen machine, the 8000-ton E8000 operating at the Husky/DaimlerChrysler Technical Centre in Novi, MI.

Can electrics dominate large tonnage?

The trend toward electric and hybrid presses is maturing in the small to medium size IMM segment, but in the larger tonnages, all-electric designs are still uncommon. One manufacturer attempting to drive the electric technology is Ube, who have launched a 1550 ton AC servo machine, with plans to eventually offer electrics up to 7000 tons. The benefits of electrics are well known, but will the current knowledge base transfer to large tonnage electric presses? “Yes”, says Chris Wild, regional manger, injection molding for Ube Machinery Inc. “If you are familiar with the transition from hydraulics to electrics, the tonnage wouldn’t make a difference. It’s simply applying the same ideas to a different scale.”

Would an electric be appropriate as a first large tonnage machine? “Absolutely”, says Wild. “If you have molding experience on any electric, large or small, it’s like riding a bike.” In terms of maintenance, electrics are different, but not necessarily more difficult: “I don’t think it’s significant, but there is a learning curve to be had. Everyone knows the weak links of a hydraulic machine. With an electric machine, troubleshooting becomes easier, but if you’re used to looking at a hydraulic system, then an all-electric machine would be a different way of looking at what’s wrong. And that would be slightly compounded on a large machine.”

Processors sourcing large electrics can choose any clamping design, as long as it’s a toggle. “The toggle clamp is really the only way to do a large tonnage electric right now, but there is still a place for all the technologies,” declares Wild. “I think you’ll probably see the straight hydraulic machine fall out of vogue faster, maybe because toggle technology is being pushed by the all-electric machine.”

Current cost premiums for electric machines in the 750 and up category are in the 25 to 30 percent range, with payback (based on energy savings of 60 to 80 percent) often occurring in two years or less, according to Wild.

Getting comfortable with large tonnages

Whatever the motive, molders moving up to large tonnage machines will likely experience a few surprises during the ramp-up to production. One is related to the sheer size and mass of the equipment. “There’s a certain amount of additional overhead that is required with large tonnage,” declares Jerry Johnson, vice president of operations for JSW Plastic Machinery Inc. “For example, the facility must be completely different than with small or medium tonnage machinery. The floor must be reinforced, and in some cases a pit is required to submerge the machine for operator safety, so that you don’t have to work on a platform. The other aspect is that all of the components required to do processing, such a part removal, is normally done by robotics because the part is so heavy. Now your overhead is twice or three times that of smaller lines.” Molders bidding on a part must take machine hour time into consideration and price accordingly. “He’ll probably charge two, three or four times the charge compared to a smaller machine,” adds Johnson.

Calculating pricing with the heavy capital costs and overheads associated with large tonnage has little room for error, especially when molding for an OEM. Move-up molders may consider hiring a consultant or consultants, especially if the job involves major changes in quality processes or EDI. JSW’s Johnson recommends consultants for molders new to large injection molding, and suggests a team approach from early in the bidding process: “If they have no experience, consultants will help. The moldmaker will tell the processor how much chilling, and what shot size they’ll need.” Johnson recommends the development of “subcommittees” of moldmaker, machinery and control suppliers to determine cycle times and overheads before the bidding process begins. “If they don’t form a team partnership, they’re going to lose. It’s a different animal altogether. The planning should start as soon as they get the part drawing.”

Winning the contract is the first step, but getting used to large part molding requires, literally, thinking big. Steve Byrnes, president, injection molding systems for HPM, relates that even as simple a task as leveling the machine takes more time and effort than a startup large part molder may imagine: “From an installation standpoint, it’s typically longer. You’ve got assembly time in the plant, but also when you think of leveling a machine, typically to level a 600 ton machine it takes about an hour and a half. To level a 2200 machine you’re sometimes looking at four or five hours. Consequently balancing and alignment of the injection end of the machine becomes more critical.” Once up and running, operating differences are also a factor, says Byrnes. “Handling of the mold is a number one issue. Most small and medium tonnage molders are not accustomed to the unique weight and dimensions of the larger size mold. A custom molder would have to be very attuned to crane capacities and loading techniques to manhandle those large tools in and out of the machine. The floor loading for the plant is substantially more, consequently, many medium tonnage plants would need reinforcing pads cut into their floors to accept the larger tonnage machines. Another item that is often overlooked when you’ve got someone used to 600 or 700 ton machines, then suddenly they buy a 2200 ton machine, is that often they have to put a foundation in.”

Byrnes also notes that filling the mold with large shot sizes is different than techniques used in smaller e
quipment. Sequential valve gating, for example is frequently necessary to achieve uniform flow across the face of a large mold. Husky’s Helmut Hock agrees, and notes that specialist processes such as gas assist are part of the learning curve as the molder bids on thin wall or high aspect ratio parts. “With sequential valve gating you are able to avoid weld lines, and you can make the part thinner. And depending on the part geometry, it can require less tonnage. Thin-walling is a trend which is continuing. I think gas assist is here to stay. Depending on the part geometry, there are big advantages with it, but I don’t think it’s something which will be used on every mold. There really are specific applications where it makes sense, as does sequential valve gating.”

No time for downtime

One consequence of the increasing trend toward outsourcing in the automotive and appliance OEM markets is that a molder is much more likely to become an assembler as well. If the resulting manufacturing cell is designed with minimal as-molded part accumulation, downstream operations are at risk if the press goes down. With tight margins and JIT delivery, unplanned downtime is becoming more expensive than ever, prompting manufacturers to build additional redundancy into controls and even hydraulics. Husky’s E8000, for example, uses an additional fourth “power pack” to provide the necessary redundancy when feeding continuous product, such as the current pilot production DaimlerChrysler Jeep TJ/Wrangler hardtop. Maximum machine downtime is targeted at 30 minutes per day.

Minimizing the risks and grabbing a piece of the growing large tonnage pie takes cash, courage and the same attention to detail which made the prospective large part molder successful in the middleweight division. And the potential for growth is at least a large as the equipment.